Heart pacemaker

ABSTRACT

A cardiac pacer features plural addressable digital memory elements each containing different pulse parameters for the pacing stimulation, address-selecting digital logic circuitry for choosing the characteristics of the pulses to be generated in response to signals derived from plural physiological sensors detecting different exercise-related body functions to improve control of the heart during various levels of exertion.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Ser. No. 06/908,367, filedSept. 17th, 1986, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a cardiac pacemaker of the type definedby the preamble to claim 1.

In pacemakers, the attempt has been made for some time for theadaptation of the pacing to physiological conditions not only to berelated to timing of the pacing pulses within the heart cycle defined bythe basic rate, but for the pacing rate itself and thus the availablecardiac output to be tailored to the needs of the patient. The previoustiming variation of the pacing pulses, in contrast, was characterizedprimarily by the attempt to avoid competition between the artificialpacing and spontaneous action.

SUMMARY OF THE INVENTION

From German patent DE-A-31 04 938 or European patent A-0 140 472,physiologically controlled cardiac pacemakers are known in which apacing parameter (AV interval or basic pacing rate) is determined bymeasured variables picked up in the heart of the patient and which varythe pacing behavior as a function of performance.

A disadvantage here is that the measured values that are picked upcannot be varied in terms of their effect on cardiac behavior, and inparticular only a simple linear relationship is available, withouttaking into account the effects of other parameters. The causalconnections in evaluating measured variables in the body forperformance-related pacing are contrarily much more complicated than isoften assumed. The linkages are entirely non-linear in nature, and theiroutcome is often not foreseeable at the outset because mayintracorporeal processes of compensation, adaptation and control aresuperimposed on one another. Above all, it proves to be extraordinarilydifficult to formulate these linkages in a closed functionallyrepresentable algorithm. This also fails to take into account the factthat pathological changes necessitate individual adaptations, andsolutions of general validity are only limitedly applicable, if at all.Nor can it be forgotten that if the sinus rhythm, as a naturalperformance-related control variable for the heart rate, is absent, thensubstantial pathological damage is already present.

In the above-mentioned known solutions, which are oriented to amonotonous connection between the measured variable and the outputvariable, the existence of a relative maximum on the controlcharacteristic curve used already leads to failure.

Moreover, introducing physiological measured variables in the signalprocessing in the pacemaker already entails difficulties because theprogramming and the adjustments that must be made for this purpose areas a rule very difficult for the attending physician to supervise, andcomplex decisions are necessary in order to adapt the pacemakeroptimally in terms of its stimulation properties to the individualconditions that pertain.

It is the object of the invention to disclose a pacemaker system withwhich the control parameters that define the function of the pacemakercan be observed and linked in a manner that on the one hand is optimallyappropriate for the desired function of the pacemaker and on the otherhand enables wide latitude in varying the parameters.

This object is attained by the novel characteristics of claim 1.

The invention is based on the awareness that with the claimed system,having at least one characteristic field, the parameters can bepresented to the physician in a clear three-dimensional perspectivereproduction by means of a suitable programming apparatus in viewableform, in which the dependency of one variable on two independentvariables at a time are prepared in graph form and can be reproduced ina three-axis coordinate system.

The system according to the invention is universally applicable forarbitrary physiological measured variables and also enables thevariables to be linked in various ways, so that further developments andexperience can also be taken into account later on by reprogramming. Thebasic equipment of a suitably prepared pacemaker thus includes aplurality of matrix-like memory regions, which are triggerable asaddresses by digitized input variables, and the values present in theaddressed memory locations--optionally after weighting--can be linkedwith other measured values read out of other memories, so that theyeither form new addresses for a further memory matrix or from a controlvariable for the pacing. The signal linkages themselves are also to bestored in memories organized in matrix fashion, so that uniformprogramming is possible by means of an external communication system.

The signal linkages in the manner of characteristic curve fields can bearranged in multiple stages, and the calibration adaptation of signalreceivers also is effected by means of such characteristic fields. Bymeans of logical associations and decision fields, predeterminedoperating ranges can be specified. With memory fields organizedthree-dimensionally, the operating characteristic curves or operatingcharacteristic fields can be represented in perspective in an externalprogramming and communication apparatus and can be varied by means ofpersonal-computer-based graphics data processing. These characteristicfields can be called up and varied successively (page-turning). Inparticular fields, the behavior can be statistically monitored overperiods of time at predetermined operating points. As a function of theoutcome of this monitoring and its frequency, the characteristic fieldscan be switched, or in other words replaced or varied in theirassociation, so that changes in the lifestyle of a patient or in theclinical picture can be addressed. In the specified operating areas (interms of the three-dimensional representation, particularly in the heartrate, stroke volume, and exertion diagram), operating characteristiccurves that individually prove to be particularly convenient oreffective can be selected, and they can also be kept in memory in avaried selection, with data access always taking place to one data setin common.

Despite the complex linkages, monitoring the function of a pacemaker ofthis kind is simple for the attending physician, because the programmingapparatus can individually represent the contents of individual matrixmemories depending on the type of characteristic fields they contain,and the memory contents can be monitored for plausibility in terms ofindividual demands. The input variables are preferably converted so thatthey form viewable variables, the variation of which in thephysiological system can be readily evaluated by the physician. To thisend, the extent of physical exertion, the heart rate, the stroke volumeand the cardiac output HZV would [sic]. Calibration of individualmeasured value pickups or the conversion of the measured valueascertained into these variables is then preferably also performed bymeans of the pertinent characteristic fields, or in two-dimensionalcalibration curves, so that measured value pickups can be individuallycalibrated.

At the communication apparatus having the graphic representationfunctions, the entire programmed system can be apprehended in the formof a block circuit diagram, and the characteristic fields applicable tothe various blocks can be made visible on the screen by "turning pages"back and forth through the files. In the memory of the pacemaker itself,only the data and their linkages are resident, while the special form ofrepresentation, including operator guidance, is generated for the userin the external control and programming part. The representationtechniques selected correspond to the known graphics capabilities ofuser programs in the personal computer field. Functions can be obtainedby selection of the pertinent fields shown on the screen by using alight pen. Characteristic curves can be marked directly on the screen inthe form of curve courses. Not only operating characteristic curves butalso permissible operating ranges can be selected by outlining theirborders.

In another preferred embodiment, the cardiac performance under variousexercise conditions is detected and processed in the manner of ahistogram (by taking an average of a plurality of events). Memories suchas those provided for pickup of the characteristic fields can be usedhere as well. In this manner the results detected are correspondinglyreadily available to the physician by using an external controlapparatus with graphic terminal functions and the detected data canoptionally be used in later operations for controlling the pacemaker.For instance, the physiological parameters that are affected by physicalexertion can be "calibrated" by subjecting the patient to a knownexertion and recording the associated control variables of the heart.

In the system according to the invention, the signals contained in thememories are processed by means of a microprocessor, and thismicroprocessor links the data contained in the memories in accordancewith a predetermined program. The kind of linkage is also programmable,and additional memory locations are provided for this purpose which arepolled by the microprocessor program. The basic program remainsidentical for all pacemaker types and programs, so that the tailoring toindividual patients can be done merely by modifying the software, sothat one pacemaker type can be used for all kinds of patients.

The programming can be done without special expertise, purely on thebasis of the causal medical relationships. The programming offers theadvantage of data variation in realtime operation, that is for thepatient, and various data sets can be compared and evaluated in terms oftheir effect. The data can be input as physical variables, so thatplausibility monitoring can be done at any time. Operator guidance andmonitoring offers security against improper use, and accesscontrols--such as those typically used with conventional programmablepacemakers--prevent unauthorized persons from changing data. A printerconnected to the attached programming system prints out the input dataand provides the documentation.

By the linkage by means of characteristic fields, specific controlcharacteristic curves can be defined, which in their linkage are alsodescribed by the content of one memory location; in accordance with anadvantageous feature of the invention, assorted variant operations canbe selected via a plurality of such data words, and the various memoriescontaining these control words are addressable externally. The system isembodied such that this (low-value) addressing can be accomplished usingconventional programming means capable of transmitting only a littledata at a time. In this way, more-thorough diagnostic programming can beperformed in a hospital setting, that is, when the pacemaker isinitially implanted, and simple adaptation can also be performedindependently at any time. One such possibility is advantageous forinstance if the attending physician has initially provided a variedcontrol rhythm on an experimental basis, which might have to becancelled if the patient has difficulties. In that case, the previousstandard program is attainable without particular effort for thepatient.

With the characteristic fields, in the linkage of their outputs andinputs, additional simple types of conditions that are not dependent onother parameters can also be programmed. For instance, simple changescan be made by having the patient lie down or stand up, or adetermination of physical activity or repose can be made by detectingmovements.

In other further developments of the invention, the measured variablespicked up by measured variable pickups and characterizing the variousphysiological parameters are subjected to an analog/digital conversion,and the digital value obtained--at least indirectly--forms the addressor an address datum for selection of the output data stored in memory,which may be stored in memory location of a variable memory so that thefunctional relationship for a set of output variables can be freelydefined by varying the memory contents.

The provisions according to the invention provide the advantageousopportunity of linking the input variables of a plurality of measuredvariable pickups for the same physiological variable to one another.This is done in that the partial addresses for addressing the memorylocations of the one memory are generated by combining the digitalvalues formed from the measured values into a common digital value.

It should be added that the tabulation of the functional relationshipnaturally need not be performed exclusively directly by the associationof pairs of values, that is, by storing in memory a variablecorresponding to the particular absolute value in the particular memorylocation; instead, the memory locations may contain instead of theabsolute value other data relating to the functional relationship--forexample in the form of a measure of increase, or of various differenceswith respect to a reference value.

Another opportunity for linking two variables relating to the samephysiological parameter is provided by subjecting the digitized value toa mathematical averaging operation and subjecting the averaged outputvalues to further processing.

By means of the above-described provisions of tabulated processing ofnon-linear functional relationships and their linkage, it is possible toprocess the physiological measured variables derived from the body in amanner that always provides the attending physician a good overview ofcurrent signal statuses.

In another preferred embodiment, in addition to the programmablecharacteristic field memories, a corresponding read-only memory is alsoprovided, which contains empirical values that can be referred to for agreat number of patients, so that if the other variable memories havenot yet been programmed, limited operation is nevertheless stillpossible. The switchover to a readout of values stored in memory fromthese various associated read-only memories can be done by varying asingle bit (memory selection bit) so that even in the event of a fault,at least emergency operation is possible.

A further problem in processing a variable derivable in the body is thatwith this signal linkage, the time-dependent course of input and outputvariables must often be taken into consideration as well. Although thetabular linkage in the characteristic field as described above doesallow taking non-linear relationships into account, it still does notallow ready consideration of chronologically prior or subsequenteffects, and so programming non-linear timedependent events would alsovery greatly limit the clarity of the data display, or might not beperformable at all, at affordable cost, because of the complexrelationships to be taken into account.

According to the preferred embodiment, a linear timing element is nowincorporated in the digital processing branch either before or after amemory addressable in tabular form, this linear timing elementsimulating one or more timing constants. The type of time constant ortime constants, or the corresponding behavior (differential or integralbehavior) of a regulating element or a delaying period is programmableby inputting the appropriate parameters. In addition to physicalrealization by means of analog component elements (active transmissionelements with memory elements and resistors, the resistors beingvariable by means of the programming), digital simulation by acorresponding computer which digitally evaluates the associatedtransmission function is preferred. In this further development of theinvention, the recognition is favorably taken into account in anapparatus that, based on variables additionally derivable in the body,forms an output signal for electrical stimulation of the heart, andsufficient precision can also be attained if the time-dependent and thenon-linear elements of the transmission functions are processed in aconcentrated and separate manner.

Such time constants take into account the fact that quantities of bodyfluid or other substances contribute to some physiological measuredvariables derivable in the body, and with such fluids or substances acertain amount of time is needed until they all uniformly assume thephysical or chemical measured variable. As an example, the bloodtemperature or blood oxygen saturation, the pH value of the blood, thesystolic intervals, and so forth can be named.

By separating the adjustment of time constants and the other tabularprogramming, it is possible, in the balancing of the valuescharacterizing the signal processing, to vary those particular valuesthat substantially characterize the particular system in a desiredmanner by suitable programming or with self-balancing of the system.

In evaluating the body temperature, for instance, for evaluation toobtain a variable characterizing the exertion of the patient, it isadvantageous, by processing the measured value for the body temperature(in digital form), to provide a differentiating component first, inorder to compensate for the integrating quantity of blood taking part inthermal conduction.

To make the apparatus less vulnerable to fault or malfunction,provisions are made that recognize faults and eliminate them in terms oftheir effect by switching over to substitute functions.

Two mesured value pickups for the blood temperature, one of which isdisposed in a peripheral region of the circulatory system and the otherof which is provided in the vicinity of the center of the body, furnishdifferent measured values if the physical exertion status of the bodychanges. In the state of repose, both pickups furnish the same valuesafter some period of time, if they are intact. In other words,monitoring can be performed even with an implanted system if the patientis examined while at rest (and optionally at different levels ofexertion) for this purpose. The monitoring of the chronologicallystationary behavior of a measured value and thus of a stationary outputsignal of the measured value transducer makes possible a component forchronological formation of a mean value, so that only those signals thatundergo limited chronological fluctuations are emitted as valid. Thusthe signals of the two above-mentioned measured value pickups for theblood temperature are redundant in the stationary instance, and theyenable conclusions to be drawn as to their function, and also enablemutual calibration.

For calibration, in addition to an ergometrically picked up signal, anadditional reference signal that is available is spontaneous action ofthe heart during operation in which there is no intervention.

A corresponding monitoring of the signals furnished by a measured valuepickup is provided by taking into account the fact that the signalsestablished in the body and characterizing physiological variables canvary only at a limited chronological rate. That is, if signal valuesdeviate to a pronounced extent from signals immediately preceding them,then once again this is an indication of a fault function.

It has already been mentioned above that various measured value pickupsfor the same physiological variable (for instance, the body temperature)may be provided at various locations in the body, to enable greaterreliability in their detection. However, in this process otherinformation is also furnished that can affect the timing control. Itmust first be noted that according to a preferred embodiment of theinvention, the signals of such measured value pickups placed atdifferent locations in the circulatory system of the body, in processingby the system shown here, are adapted to one another prior to beingunited, in a manner suitable for the physiological conditions. By meansof a suitable time constant and by means of a relationship--optionallynon-linear--that can be stored in memory, a portion of the physicalregulating system of the body itself can be simulated.

The calibration can preferably be performed with the system shown here,in such a manner that a pacing rate is first established at stationaryexertion, this rate corresponding to the applicable exertion level, andthe natural cardiac activity of the patient at earlier times can also beutilized for comparison.

In other advantageous further embodiments of the invention, it isfavorable to provide other--optionally external - measured valuepickups, which by means of interactive communication of the programmingmeans are connected to the system shown here for information exchange,and in the context of the complete programmability of the system, thelinkage of the signal flow routes or the influencing variables are alsopre-selectable. In this manner, the behavior of an already-implantedpacemaker can be adapted both to further discoveries by the attendingphysicians relating to the patient in general, or to the further courseof the clinical picture, but additionally progress in medicalapplication of the technology shown here can also be taken into accountsubsequently as well. The technological realization of theprogrammability of the linkages is preferably effected in such a mannerthat an additional memory in the manner of a matrix is provided, inwhich memory locations are provided for a number of the aforementionedcomponents (tabular memories, time constant memories, linkage modules,mean value formers), and these memory locations hold the addresses ofthe memory locations in which the input or output data for these modulesare to be stored.

The parameters characterizing the electrical stimulation, or pacing, actwith variable intensity on the pacing behavior of the pacemaker, and thepacing is preferably influenced such as to adapt cardiac performance tocurrent physical exertion.

A component connected to the output side of the last linkage elementserves to adapt the variable that affects pacing of the heart in such amanner that the cardiac performance varied by the pacing (preferably viathe pacing rate) is adapted to the parameters detected physiologicallyin the body only within the particular performance range that the heartof the patient is capable of encompassing.

It is apparent that by means of the system shown here, the entirereaction and control behavior can be programmed and monitored in aviewable manner and in a form accessible to the physician.

Adaptation to particular forms of therapy is possible withoutdifficulty, and for instance in the ischemic heart, the rate ranges inwhich the heart demonstrates adequate functional capacity can be"dialed" in a purposeful manner by programming, by means of pacing atthe appropriate rate in the case of non-spontaneous cardiac activity, sothat during operation, the particular "functionally capable operatingranges" of the heart are searched for and located based on thenon-linear properties of the system.

Advantageous further developments of the exemplary embodiment aredefined by the dependent claims and described in further detail in theensuing description, in terms of a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the system structure of an exemplary embodiment of theinvention;

FIG. 2 shows a characteristic field used in the memory region of theexemplary embodiment;

FIG. 3 shows the elements existing in a signal processing module,including a characteristic graph according to FIG. 2;

FIG. 4 shows an arrangement of signal processing modules forprogrammable linkage;

FIG. 4a shows an auxiliary module for signal storage and linkage inconnection with the arrangements of FIGS. 3 and 4;

FIG. 5 is a block diagram for a cardiac pacemaker realized according tothe invention with the aforementioned modules;

FIG. 5a is a diagram explaining the cooperation of the communicationunit with the modules of FIGS. 4 and 4a; and

FIGS. 6a6e show various characteristic graphs in three-dimensionalviews, for explaining different variants of the exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the exemplary embodiment described below of a cardiac pacemakeraccording to the invention, various components serving to perform signalprocessing and described as matrix-organized memories or memoriescontaining characteristic fields are used multiply in similarconfigurations, so that for understanding the invention it will sufficeto describe these basic components generally in terms of their function.In the descriptions of the functional cooperation of the apparatus as awhole that are given below in conjunction with the block circuitdiagrams, it will accordingly not be necessary to describe the functionof these components in detail.

In FIG. 1, first, the basic design of a cardiac pacemaker is shown, withmeans for processing at least one input measured variable forphysiological variation, preferably of the heart rate.

On the input side, accordingly, at least one measured value pickup isprovided for a measured variable that can be picked up inside or outsidethe body; this variable can be utilized for physiological control of thepacing rate or--in the case of a demand pacemaker--of the basicheartbeat interval. These variables are of the type that differ fromsignals electrically derivable in the heart, and they serve only toprevent pacing in competition with spontaneous ventricular actions or tosynchronize the pacing pulses, and they relate only to a current heartaction. Correspondingly, all the pacing variables can be varied inaccordance with the "physiological" input variables for which arelationship for a pacing behavior can be found that is valid over aplurality of heartbeats. These input variables, in turn, are allvariables that are relevant to pacing and that are not related to merelyone specific cardiac action but rather pertain in general to the pacingbehavior. Among them are also the parameters that in pacemakers are"programmable", as well as others to be discovered in future, whichimprove the pacing behavior--measured in terms of the intendedfunctional capacity of the heart.

Corresponding measured value pickups are known in principle, in the formof temperature-dependent variable resistors for measuring the bloodtemperature, measuring electrodes for ascertaining impedancecardiographic (electro-plethysmographic) data, photoelectric measuredvalue pickups for ascertaining the blood oxygen saturation by means of abeam of light or light gate, chemical sensors for ascertaining the pHvalue, or pressure or sound pickups for measured values that have arelationship to mechanical contractions. In particular, the measuredvariables picked up in the heart itself, and which form a standard forthe chamber filling, and thus are already linked with a variablecharacterizing the cardiac output--and hence the functional capacity ofthe heart--can advantageously be utilized for varying the pacingparameters (in particular, the heart rate).

Additional physiological measured values can also be obtained from theelectrical voltage potentials picked up from the heart, however, such asthe Q-T interval, which can also be used to control the heart rate.

In the ensuing description these variables will be called "physiologicalmeasured or input variables". A pacemaker that processes a plurality ofinput signals can accordingly be called a "multi-physiologicalpacemaker".

The analog output signals of the measured value pickups are eachsupplied to an analog/digital converter connected to their output side,which converts the input signals into corresponding signals that areprocessable with the digital memory means or signal processorsdescribed. The processing of the data words, each forming a measuredvalue, is effected by means of a microprocessor and its peripheralmodules for data storage and data processing.

In the exemplary embodiment shown in FIG. 1, the physical (i.e.,hardware) structure of the pacemaker system described below is shown.This is a microprocessor system 110, which is capable of bidirectionalcommunication with an external control unit 125, as a programming unit,by means of telemetry.

The implantable unit contains a conventional multiprogrammable system111, which enters into interaction with the ventricle and/or atrium viaone or two electrodes. As an interface with the rest of the pacemakersystem, a parameter memory 112 is provided, which at the same timeserves as a buffer for data exchange with the conventional pacemakersystem. Contained in the parameter memory are, first, those data thatare prespecified to the pacemaker 111 as operating parameters or inother words control variables. These variables form the values of a one-or two-chamber pacemaker that are adjustable by external programming,and the operating mode (from V00 through DDD) is likewise programmable.

Also contained in the memory 112 are operating parameters of the kindthat are picked up in the patient's body by further measured valuepickups and are derived from "physiological" input variables. In thecase of the Q-T intervals, however, they can also be derived via thepacing electrodes themselves.

While the pacemaker system 111 itself thus contains those circuits thatprevent competition of pacing events with spontaneous pulses, themicroprocessor system encompassing this block serves to define furthercontrol variables, preferably the basic rate, and in this sense toexpand the system 111. This has the advantage that for using the system110 in the conventional manner, no additional skills are required beyondthose necessary in the use of known multiprogrammable pacemakers.

The pacemaker 111 is capable of operating even without "physiological"picked-up measured variables, the basic pacing rate being predeterminedby external programming as in conventional pacemakers. Depending on thetechnological realization, the necessary signal and data processing forthe operation of the pacemaker portion 111 can also be performed by theCPU 113 of the microprocessor.

Associated with the CPU 113 are a random-access memory or RAM 114 and aread-only memory or ROM 115 as well as an input/output unit 116, bymeans of which the data traffic with the peripheral components 111 and125 is carried out. It should be noted that with the system shown,signal processing is done in the manner described below, and thememories and data linkages described below are generated by suitableprogramming, that is, by software, and are already present in the RAM orROM memory areas. The system is perceived by the user as if it were anapparatus having the described physical structure, which can also berealized by hardware provisions. To avoid having to describe thechronological sequence in the processing of programs in typical dataprocessing structures, which is dictated by the solely serial processingperformed by the CPU in a microprocessor system, the description herewill be made as if the various memories were generated separately ashardware and were connected to the control and data transmission linesthat represent the flow of data in the block diagrams.

Connected to the input/output unit 116 is both the parameter memory 112and various measured value pickups 117, 118, 119, 120, which viadigital/analog converters 121-124 deliver the picked-up signals to theunit 116. The signal pickups were mentioned at the outset above and aredisposed in or on the patient's body--in particular on the pacingelectrode or on the housing of the pacemaker itself.

The signal processing done by the CPU is serial, and the individualcomponents of the structure to be described below are optionallyincluded in the data exchange in accordance with appropriate interruptcommands, so that the signal processing--adapted to the temporalcommands of the signals--is performed in a clocked, quasi-simultaneousmanner.

By means of the control unit 150, a data transfer from and to theimplanted unit is effected via a telemetry component 151, whichcommunicates with the corresponding telemetry component 125.

The control unit has its own CPU 152, which exchanges data with its ownRAM memories 153 or ROM memories 154. An input/output unit 155 is alsoprovided, to which the telemetry unit 151 and a video interface 156 areconnected. The video interface is connected to a monitor 157, which inaccordance with the program present in the external unit 150 makes itpossible to call up data from the implantable system and vary thesedata. It is particularly significant that the entire operation by theuser and the means for graphic display are present in the external unit,including data relating to the general structure of the implantablesystem. By graphic display of the data obtained and of the findingsnecessary for programming the internal system, a comfortable mode ofoperation is provided which provides the operator with information onthe operating state of the implantable system at all times. Programmingis done by means of a light wand 158, with which data can be selected bycontact with the screen. Correspondingly, a pressure-sensitive screencan be used, in which the selection of information is possible bytouching the surface of the screen. In accordance with the knowntechniques of graphic image processing, a selection of screen pages(corresponding to "paging through" a card file), and both duringoperation and in evaluating the data ascertained during operation,presentation is preferably done in graphic display using internationallyunderstood symbols. The individual function regions of the implantablesystem can be dialed separately, and a search tree structure leads fromthose parameter ranges that pertain to the basic functioning of thepacemaker to more-subtle linkages, and this structure is attainable withvarious access codes to a depth assigned to a particular user. By meansof a printer 159, a protocol can be printed out for documentationpurposes.

The external form of the components 110 and 150 is also shown in FIG. 1,showing that the implantable part has the dimensions of a standardpacemaker 160, while the external communication part 161 has not only anantenna part 162 that can be placed on the head of the patient but alsoa graphic display surface 163.

The ensuing description relates to details of the component 116 andespecially to the linkage of the "physiological" input variables of themeasured value pickups 117-120 as well as to the data linking and thecontrol thereof.

In FIG. 2, the matrix-like memory structure of a characteristic fieldprovided for controlling the system is shown, and the memory locationsof the matrix can be addressed by column and line address signals, andthe numerical value present at the addressed memory location can be readin or out. Each characteristic field is addressable by means of a commonaddress characteristic, so that on the one hand a simplified addressingis possible in normal operation, but on the other hand a newconfiguration of the processing and a self-contained reading out or achanging of the contents of one characteristic field can readily be donein connection with the external communication unit.

While in normal operation a linkage of the address inputs and datainputs or outputs is done in accordance with a predetermined linkingplan, where in preceding characteristic field memories, data read out byaddressing serve to address successive characteristic field memories,these data can also contain information which relate to the linkage ofthe data with successive characteristic fields themselves, either interms of the direction of the linkage or in terms of the operations tobe performed (logical or mathematical) in the linkage. The correspondingdata contents differ from one another in additional attributes, whichcan be distinguished in suitable subsequent data discriminators (notshown). During the external communication, by means of the commonaddress characteristic of each characteristic field memory, directaccess to the contents of the particular total memory region is possiblefor reading data in and out or changing data. The characteristic fielddata for the data processing preferably have access addresses, which canbe called up similarly to those of auxiliary memories, and which containsolely linkage, selection or other auxiliary information such as datasets that can be read out from the communication unit with graphic dataor specifications for the particular pacemaker type.

This direct access is represented in FIGS. 2 and 3 in the lower part ofeach of the drawings by the control and access plane 306. Accordingly, adata field may be not only a module of the signal processing, in thesense of linking input and output signals but may also be a memory, theinformation in which form for determining the sequence in terms ofcombining together input and output data of various characteristic fieldmodules.

The memory unit shown in FIG. 2 need not--as shown--in this form embodya physical or hardware-type unit in the memory region of the system. Thepertinent structure can also be generated purely by software.

The memory unit of FIG. 2--which here is also synonymously called the"characteristic field memory" or "memory matrix"--forms a part of a"cell" shown in FIG. 3 as a signal processing module, in which thememory unit is also surrounded by auxiliary components, which arefavorably provided in a modular structure in each charactristic fieldand which are linked along with them in the network formation, so thatonly the inputs and outputs of this cell appear as interfaces. Modulesnot needed in a particular application are each rendered inactive by theloading of appropriate control parameters in the auxiliary memory (aswill be described hereinafter).

The combining of the signals of various measured value pickups iseffected in a block 301, taking into account the weighting signalassigned to each signal of each measured value pickup. The block 301also at the same time forms a switch component, which via the accessplane 306 selects various signals as input (that is, address) signalsand depending on the "switch position" (influenced via the selectioninformation of the control plane 306) links various signals by means ofthe following characteristic field for the variable addressing of theoutput of signals from the following characteristic field memory 302, inthe form of digitized amplitude data. The selected input signals eachform partial address signals, which taken as a whole encompass thememory range of the following characteristic field. By means of linkingdata to be supplied separately to the block 301, the input data can notonly be switched but also (individually or in common) subjected tological or mathematical operations; that is, data can be selected,shifted or in some other way "processed". In particular, operatingranges or operating characteristic curves can be selected in this way,and the selection data, which characterize authorized address regions,are stored in a suitable characteristic field.

With parallel addressing of the memories containing the signal data andthe selection data, and linking via block 301, the selection data (forexample by means of an AND linkage called up via the control plane 306)characterize only signal data that have a data value deviating from"zero" as authorized addresses. The selectable address range can thus berestricted or affected in some other way arbitrarily. Preferably, alimited number of linkage operations that are to be used often are heldin reserve for this purpose such that they can be called up directly viathe control plane. Input variables can also be subjected to more-complexoperations by means of a correspondingly programmed characteristic fieldmemory, which authorizes any evaluation of input signals by means of acorresponding specification of output signal values as data values inthe pertinent memory locations addressed by combination of the inputsignals. On the other hand, input signals can also be subjectedexclusively to illogical linkage in the block 301, with the followingcharacteristic field either being "bridged" in terms of data processingby a corresponding control signal (not shown), or it is renderedineffective by the pertinent characteristic field by storing theaddresses in the memory locations, so that the input signals appeardirectly once again at the output of block 302.

The control plane 306 itself can--as also shown hereinafter, referringto FIGS. 3 and 4a--be reached by output signals of the characteristicfield memory 302, so that as a function of signals contained incharacteristic fields, the signal linkage can be influenced via theblocks 301. A data set contained in a corresponding memory 302accordingly includes not only an instruction as to whether it is signal,selection, or linkage or other auxiliary information, but also in thecase of selection information the designations of the pertinentcharacteristic field cells that form the output and input for the signalto be processed. In the case of linkage information, the agreed-upondesignation of a logical or mathematical operation is also included.

Additionally, as a function of data addressed in characteristic fields,a plurality of data linkages can also be affected in the overallstructure of the system. These are stored in fact by means of linkagememories--as will be described hereinafter. If such a linkage memory iscalled up, by means of a signal contained in a memory location, thesystem structure changes more or less fundamentally. In this manner, thecardiac pacemaker described is "self-teaching" in such a manner that theconfiguration of the processing can be predominantly automaticallyadapted in terms of the measured value selection in processing to theinput signals found and to their changes. Such changes are in particularthe following: the shutoff of malfunctioning measured value pickups, andin this connection in particular the transition from operationdetermined by a plurality of physiological measured value pickups to themode of operation that is influenced by one such pickup, or by no suchpickups. While two measured value pickups for the same variable canoften be operated in differential operation, a single remaining pickupcan often--given a suitably increased error probability--contributeeffectively to control as well.

Together with the data signals, evaluation numbers are also carried inthe processing, which in an evaluated combination contain a conclusionas to the value of an input signal in terms of its expected reliability.The evaluated combination is preferably performed with standardizedinput signals. It links input signals containing identical informationto form one combined output signal, which is done in accordance withmathematical laws for the formation of mean values of measured valueshaving weighting. This mean value formation can be effected either bydigital processing, via calculation in accordance with a relationshipexpressed in a formula, or by means of a table storable in memory in theform of the characteristic field memory. To ascertain the weight of thepertinent input signal, additional evaluation of the pertinent signal interms of inherent faults are expressed by unexpected fluctuations orsuperimposed amplitudes. The corresponding malfunction recognitioncircuits correspond to circuits such as those already used for theelimination of faulty input signals in medical electronics.

Accordingly, digitized data of various types are supplied to thecomponent groups 301. In detail, the data of one input plane each arecombined following a linkage that can be predetermined via the externalprogramming access plane 306. The input signals serve to address thelines of the characteristic field memory 302, and the data G₁ -G₃ serveto address the lines, while the data 1-3 relate to the datacontents--that is, the data to be written into the individual addressedmemory locations.

Via the external control (access or programming) plane, the type oflinkage in the memory 301 can be predetermined, and various mathematicallinkages (summation, multiplication) or logical linkages can beselected, so that the data can be added, multiplied or otherwisetransferred in accordance with a logical condition; the logicalconditions may comprise not only AND, AND/OR or other known linkagesperformable by logical gates, including "greater than", "less than" or"equal to" relationships. It can also be predetermined that whilesatisfying the predetermined condition a particular fixed logical valuewill be output. The component group 301 accordingly allows theprocessing of signals with either a fixed logical level or with avariable level in digital representation.

The number of planes of the component element 301 increases accordinglyif the characteristic field memory 302 is embodied multidimensionally,as indicated by the perspective layering in FIG. 3. For each dimension,an additional addressing plane is required. The illustration in FIG. 3is accordingly more symbolic in form. Any other suitable embodiment ofthe actual memories is also possible.

Following the circuit 302 is a programmable signal processing componentgroup 303, which enables a time-dependent linear processing of thesignal value, while in the component group 302 a non-linear, tabulatablerelationship between the input and output variable is present in theform of a characteristic graph. The two component groups 302 and 303 areto be influenced by external programming means via the control plane306, and preferably the coefficients of a linear differential equationdetermining the chronological transfer behavior (in a similarlymatrix-like arrangement corresponding to the other data componentgroups) are preferably capable of being fed into the component group303. The chronological processing is done by means of the internalmicroprocessor in accordance with such systems that by digitallyadjustable parameters enable the digital simulation of linear physicalsystems. By the separation of non-linear and linear system components ofthe signal processing, a simple system structure is obtained with simpleadaptability, and the system is uncomplicatably adjustable externally.

The signal processing portion 303 may also effect a signal delay in sucha manner that by means of a certain parameter, a predetermined signaldelay is predetermined (by the designation of the corresponding numberof clock signals of a system clock), and thereupon the output signalsappear delayed at the output, as compared with the input, only by theindicated number of clock signals, the delay being in accordance withthe set number in the manner of a digital delay line (shift register).The representations shown in block 303 provide examples of a possibletransfer behavior, which is described by the characteristic values ofthe pertinent linear differential equations.

The component groups 304 and 305 generate an identification for thereliability of the signal emitted by the component 300, which issupplied to the input of the following corresponding component, so thatin each state a standard for the reliability is provided, which can betaken into account in the ensuing combination. Faulty signals can beeliminated in this manner, so that in the ensuing processing, access ismade instead to other, error-free signals.

Thus it can be ascertained whether the pertinent input is associatedwith faulty signals. An indication of this occurs if with measuredvalues which are inherently subject to a slow change (blood temperature,etc.), signals arrive for processing that have an abruptly changingcharacter. Furthermore, one criterion is that in the comparison of twoor more signals which under certain conditions exhibit an identicalcourse of change, deviations from this identical course occur. Animportant fact for processing with the pacemaker described is that inthe form of an additional datum of at least one bit, an identificationrelating to the reliability of the corresponding measured value--or inaccordance with the time-dependent processing in a component 303--isadded to the digital input signals, for a linkage of measured values.

In the simple case for error recognition, the weighting apparatus 304includes a mean value former and a comparator, to which the input signalfrom the component group 301 is supplied directly and the output signalof the error recognition is also supplied, and if the input signaldeviates beyond a predetermined amount the output signal of theweighting apparatus 304 indicates that the input signals possibly haveonly a reduced reliability, so that the weighting in the evaluation isto be decreased accordingly. The signal G combines the weighting signalsof previous stages, which stages have already performed respectivecorresponding evaluations. In the component group 305, the signal G isadded to the output signal of the stage 304, and the evaluatedcombination is made available to the stage 300 as an output signal. Thecomponent groups 304 and 305 can likewise be switched via the controlplane 306, as well as in accordance with signal data and by means ofexternal programming.

The "cells" containing characteristic fields may contain variant kindsof information. For example, they form read-only memories even withoutlinkage of their data contents with other cells, and they areaddressable by means of physiological measured values or output signalsof other characteristic value memories. In this manner, regions that arerun through by the (address-forming) input signals can be particularlyidentified for subsequent stages or for external communication withgraphic representation. Authorized operating ranges or emphasizedranges, or logical linkages on the other hand, can be predetermined. Ifthe memory contents, as output signals, are not intended for subsequentmemory cells for addressing or as data signals, such characteristicfields can also serve merely for the information of the user or forcontrolling the communication system, in order to emphasize particularoperating ranges for the external communication in the graphics usedthere.

In FIG. 4, the arrangement of the above-described component groups in amatrix-like structure is shown, in a manner that is the basis for theaddressing of the individual component groups in the context of theirlinkage in a linkage memory 406. For the association of the selection,they can also be presented correspondingly graphically. A function groupaddressable by means of line and column numbers includes the functionelements, of a cell selectable as such by addressing, comprising asumming portion 402, characteristic field 403, linear time element 404and weighting unit 405 (corresponding to the illustration in FIG. 3).These function groups are repeated in an arbitrary line and column grid,and by means of two memory ranges organized in matrix fashion on the onehand for each functional component group in terms of its inputs, the"map square" of that particular component group the output signals ofwhich are supplied to this component group can be input. Since thesumming unit 402 has a plurality of inputs, a plurality of columns andaddress identifications can be provided for each component group.

Additionally, the output signal data can be associated with thefollowing cells, as described above. In the outermost column on theright of the memory 406 receiving the linkage information, for example,the input variables of the pacemaker system are each assigned to onememory element of one line, so that by means of the corresponding inputit can be determined whether the output signals of which component groupshould form the pertinent parameters. The first memory 406 contains thesignal linkages valid in normal operation--in a manner programmable bythe external communication portion.

In a second memory 407 organized in matrix fashion, the system structurefor an alternative operating state, such as can be called up by thesignal data themselves via the control plane 306 (409), is shown--onceagain in column and line association.

In FIG. 4a, it is shown how by linking two characteristic field cells410 and 411 (corresponding to the cells 401 in FIG. 4) and one countercell 414, a histogram memory is formed, can, which upon later being readout provides information as to behavior of the pacemaker system.

The cell 410 here forms a (programmable) reference field, in the memorylocations of which, which are addressable by means of output signals ofpreceding cells or by input signals, values are stored that serve asreference variables in comparison operations. In a counter matrix 411,counter states are stored in the individual memory locations, which onceagain are organized in matrix fashion, the counter states representingthe appearance of particular events--in the normal case, the exceedingof or failure to attain the corresponding reference value contained inthe cell 410. The memory cells 410 and 411 are addressed in parallel forthis purpose. The input signal which is to be compared with the valuesstored in the reference cell 410 is supplied to a comparator 413, whichcompares it with the particularly addressed signal in the reference cell410 in accordance with an externally predeterminable condition. If thecondition is met, then by the single occurrence of this state(controlled by a clock signal), the value present in the addressedposition after the output of the counting memory is raised by one andread in again. In this manner, a characteristic field to be read outlater is produced, which in the graphic representation indicates thefrequency with which predetermined operating values are attained.

The possibility of varying the operating behavior of the pacemakertaking into account the frequency with which predetermined operatingvalues are adhered to as well is also provided. To this end, preferablythe contents of the counter characteristic field 411 of FIG. 4a issupplied to a block 300 shown in FIG. 3 as an input variable, and theoperating behavior is varied in accordance with corresponding logicaldecisions by means of a corresponding characteristic field. To this end,the characteristic field matrix addressed on the basis of the counterstate (behavior in the past) is followed by a further characteristicfield memory for the call up of different characteristic fields, whichvary existing linkages (linkage memory 406 in FIG. 4, or affect theparameter memory (112 in FIG. 1) or correspondingly switch over orreplace characteristic fields serving as read-only memories. To thisend, it is favorable if the parameter memory 112 which influences theconventional behavior of the pacemaker is likewise designed inaccordance with the characteristic fields that monitor the physiologicalcontrol. In this manner, it is also possible to program the conventionalportion in accordance with the processing of the physiologicalparameters.

"Physiological" measured variables, which are ascertained in theconventional portion of the pacemaker, such as the Q-T interval or aspontaneous frequency occurring at particular states of exertion, canthus be transferred into the remaining system via the parameter memory112 as an interface. This interface is also suitable for the transfer inascertaining physiological variables via the electrodes or othermeasured value pickups provided in the conventional region of thepacemaker.

Via a corresponding control of the control plane 306, a switchingelement which as a function of the output signal of block 411 emits asignal to the control plane, which signal influences a linkage matrix406 which in turn again triggers the block 301 (in FIG. 3), can beconnected to the output side of the block 411 (or any other componentgroup). In this way, as a function of the previous behavior--optionallyalso to be averaged over predetermined time segments--the futurebehavior can be influenced. Characteristic fields can be switched over,or in other words exchanged, evaluated differently or changed in theirlinkage with preceding and subsequent characteristic fields. How thesechanges should be made is stored in the characteristic fields involvedwhich store the linkages. The system is thus likewise "self-teaching",and a change in the configuration is not done until there is a certainfrequency of events. A standard for the change of the system behavior isfaults of a predetermined frequency or intensity, or the non-occurrenceof predetermined operating states, which from the standpoint of therapynecessitate a certain pacemaker configuration, so that the pacing canalways be done in the simplest kind of operation--and the one easiestfor the physician to monitor. Thus the physician is also capable ofusing the memory for monitoring success of the programming he hasperformed.

Now that the basic component groups have been described, the cooperationof these component groups will be described in further detail referringto the block circuit diagram of FIG. 5. Particularly important for theoperation of the system is the fact that the signal variables are linkedin accordance with their physical or physiological significance. Inaccordance with a calibration table (characteristic field) connected tothe output of the relevant measured value pickup, a conversion into avariable adapted to the current performance deficit of the heart is noweffected in a further processing cell. A differentiating component isassigned to the blood temperature, since a rise in temperature alwaystakes place with a delay as compared with the current exertion level. Anincrease in exertion beyond a predetermined value is limited in time(the contents of the counter matrix 411 in FIG. 4a is raised by means ofa system clock serving as a time clock). When a predetermined durationof time is exceeded, the emitted exertion variable is lowered by meansof a corresponding switchover of the pertinent characteristic field viathe control plane, until the temperature again attains a lower outputvalue. In this manner, in a fever condition a permanent increase in theheart rate is avoided.

The physiological variables picked up in the body are each linked oncorresponding "linkage planes" with the further identical signals, sothat a physically correct further processing takes place. Between twolinkage stages (if necessary), an adaptation of the temporal andamplitude behavior of the signal to be processed and linked isperformed, so that the pertinent signal is adapted at the particularlinkage location with a further physiological variable, which is ofsignificance in controlling cardiac activity. The advantage is thusobtained that the system can operate parallel to the signals takingtheir course in the body and calling up a variation of the cardiacactivity and parallel to the endogeneous regulation processes, and inthe various linkage stages the particular pertinent physiologicalsignals are likewise ascertained at the pertinent stage by additionalmeasured value pickups and are usable either as monitoring signals orare incorporated in accordance with their value into the further signalprocessing. A separate characteristic field memory is provided for the"calibration" of each of the measured value pickups.

A further factor is that signals which on the one hand are standard forthe performance required and on the other hand are jointlycharacterizing for the cardiac output itself, as well as variables thatare only briefly available (monitoring measurement of physical exertionby means of an ergometer for the sake of calibrating measured valuepickups) are likewise fed in in a system-correct manner and enable aconclusion to be made as to the processing capability of the precedingstages, or permit correct setting of the corresponding processingparameters (components 302 and 303). Furthermore, by feedback of avariable that enables drawing a conclusion as to the cardiac performancecapability, the signal processing can also be influenced. This feedbackis done in such a manner that the physiological measured values in theprocessing are combined and converted in such a manner that they form astandard for the instantaneous requirement of the cardiac output. Acriterion for the actual cardiac output derived from the heart isutilized as a comparison criterion, this cardiac output being taken intoconsideration as feedback in the selection of the pacing rate in thecontext of the table. In a preferred embodiment, the table establishingthe pacing parameters is updated based on the cardiac output actuallyestablished with the pacing using the pertinent parameters. In the caseof input addresses that require a particular cardiac performance, theparticular pacing parameter, or signal values that lead to the necessarypacing parameters, are entered.

For the linkage of signals in the form of digital characteristic field,the following basic principles--depending on the applicationsmentioned--arise:

1. Pure control functions are formed by simple linkage of input measuredvariables of address variables and by the pacing parameters as storedvalues.

2. Regulation functions are realized in a corresponding manner, withmeasured input variables being converted by corresponding characteristicfields into a variable that is representative for the physical exertion,in accordance with the required cardiac output. This variable addressesthe characteristic field together with a variable representative of thecurrent stroke volume, and the then necessary heart rate can be read outof the individual memory locations. In particular, instead of thevarious absolute values, the particular deviation from a predeterminedset-point value is usable as a signal value, and the ensuing processingthen likewise relates to the corresponding deviations. In the case ofmeasured variables which follow the actual physical reference value witha temporal delay, a compensation is preferably provided where thepertinent measured variable is present in the most unadulteratedpossible form. The temporal delay in the rise in temperature of theblood during physical exertion is compensated for by differentiatingcomponent (303 in FIG. 3), so that the rate change begins more quickly.

3. The calibration of a measured variable dependent in particular onexertion is effected by providing that in the calibration period, thevalue expected (and optionally ascertained by a different measuringmethod) is respectively written into the memory location addressed bythe current measured variable. In particular, to this end the exertionascertained externally by means of an ergometer is written into a memoryto be addressed by means of the measured variable or variablescharacterizing the exertion, in each case in form of a value. This valuein turn, during the subsequent operating state, addresses thecorresponding rate in a characteristic field, and this rate is selectedsuch that (in particular in the case of combined addressing with ameasured value representative of the current stroke volume) the productof the stroke volume and the rate, as the cardiac output, corresponds toand is followed up with the ascertained current exertion variable.

4. The error control is ascertained by comparison of two (or more)variables. The pertinent characteristic field effects a shutoff of oneor all values, in the case of deviations that are greater than apredetermined extent. In the addressing of memory locations,correspondingly, with three comparison signals the particular signalthat deviates substantially from two others can be excluded from furtherprocessing. To do this, a characteristic field is needed which isaddressed by address signals in which all three address components arecombined. Three different signals acting as shutoff commands arecontained in the various memories addressed by the unauthorized signalcombinations, and in the event of a deviating signal preclude thissignal from further processing, and in the case of two deviationspreclude all three signals from further processing. Furthermore,(optionally in accordance with further signals), expectation values canbe predetermined, which permit further processing of the input signals(by logical association in a corresponding characteristic field memory)only whenever the input signal is within a predetermined expectationinterval.

5. In the control plane, a selected operating characteristic curve ispredeterminable (for example by external communication), in such amanner that in an additional characteristic field (addressable by onlyone input variable) the value is firmly associated as memory contentswith the other variable. This can be done for example by means of acalibration process (as indicated above). The second characteristicfield is then merely "one-dimensional". In a perspective (graphic)representation of a two-dimensional characteristic field, the points onthe operating characteristic curve can also be represented such thatthey are graphically emphasized, by superimposing the one-dimensionalcharacteristic field. With one operating field, a corresponding regionof input signals in a characteristic field is declared allowable, bymeans of corresponding memory contents and subsequent logical linkages,and delivered for further processing.

In FIG. 5, a pacemaker system as it is presented to the attendingphysician on the screen of its control unit is shown in block form. Atthe same time it represents the basis for the functional description ofa pacemaker system of a kind that can also be generated in aconventional manner--for instance by means of hardware. FIG. 5 shows theimplantable portion, and the pertinent arrangement is naturally notrestricted to implantable systems but is also applicable to externalpacemakers correspondingly. The block 501 shown in dashed linescharacterizes the regions of the human body located outside the heart,from which physiological measured variables are derived that pertain tothe function of the pacemaker, while the heart 502 enters intointeraction with the system via the pacing electrodes and measured valuepickups emplaced in the heart.

A conventional pacemaker 503 is capable of functioning autonomously andis optionally multiprogrammable via a programming unit 504. (In a systemshown according to FIG. 1, which represents the real linkages, theprogramming is done by means of the unitary control unit by means of theparameter memory 112.)

In the system presented graphically to the physician as shown in FIG. 5,the programming is done with a block 504, which can be called up on thecontrol unit in the form of a page and contains the conventionallyprogrammable parameters in the usual designations. Selectively,different types of pacemakers can be implemented completely here. Thetranslation of the real parameters set in the implantable system into aconventional system is done in the external control portion, and aselector switch is provided which permits different kinds ofimplantations.

The blocks outlined in solid lines are component groups according toFIG. 4, which contain the function elements of FIGS. 2 and 3 and arelogically connected in the manner shown by means of the linkage matrixindicated in FIG. 4. The exemplary embodiment according to FIG. 5 showsexemplary types of linkages in a preferred embodiment, the operatingmode of which will be described in further detail hereinafter. It isapparent that the output signals of various analog measured valuepickups 505-509 in the block diagram are linkable in different groups inthe course of the signal processing. Previously, a conversion of theanalog input variables was done by means of analog/digital converters510-514. The output variables of the converters are suppliedrespectively to evaluation component groups 515-519, in which anindividual, or in other words programmable, adaptation takes place. Thisadaptation, by corresponding programming of the characteristic fieldshown previously, includes the elimination of non-linearities of themeasured value pickups, enables the programming in of time-dependentchanges of the transfer characteristic and of weighting factors. Thusthe transfer behavior of a measured value pickup can be changed by meansof the characteristic field programming.

While the measured value pickups 506 ascertain the partial pressureO_(RV) of oxygen in the right ventricle or the respiration rate, themeasured value pickup 507 serves to ascertain the blood temperatureT_(B), preferably in the vena cava. While the partial pressure of oxygenor the respiration rate is a good standard for the instantaneous oxygendeficit--presuming a suitable calibration of the correspondingcharacteristic field--the blood temperature has an integrating characterand rises or falls only after a certain time delay. In order in thecomponent 520 following and identical to the blocks 516, 517, whichcomponent 520 links the output variables of the precediang blocks withpre-programmed weighting (with an exertion variable obtained as anagreeing reference base), inside the component 517 the time constant isprovided by corresponding programming with a differentiatingcharacteristic, so that preferably the differential changes of the bloodtemperature as a standard for a state of activity or repose are linkedwith the output variable of the block 516.

The superposition can be done either by weighted sum formation,linearly, or by means of a characteristic field, and in the case of atwo dimensional characteristic field one input variable each addressesone coordinate axis. The linkage in the component 520 is also dependenton sensors 521-523 emitting a number of digital output signals, whichsensors--as described above referring to FIG. 2--effect switchovers ofthe characteristic field present in the block 520. Thus a mercury switch521, which is implanted along with the pacemaker housing, recognizes theinstantaneous position of the patient (lying down, standing up) andthereby furnishes an additional possibility for evaluating the exertionof the patient. A digital activity sensor 522 furthermore recognizes, bythe appearance of accelerations and decelerations beyond a predeterminedthreshold value, whether the patient at the time is generally at rest orin motion and switches the characteristic field located in block 520over accordingly. The control of the measured value processing isaffected by means of a common system clock, to assure synchronism.

A digitally operating error recognition means ascertains whether anexertion variable at the time can just then not be ascertained. Forinstance, if the respiration rate is picked up by means of a microphone,then by means of an additional microphone present in the errorrecognition unit 523, loud noises originating in coughing by the patientor the like are recognized and utilized for blanking out the measuredvalues of the pickup 506, which could be done by switchover of thecorresponding characteristic field, or also be reducing the weightingfactor by connection with the block 516.

An additional measured value pickup 505 forms a recognition for theactivity of the patient with an analog output signal. In accordance withthe component 522, the acceleration and delays are ascertained in termsof amplitude and frequency and processed further via the componentgroups 510 and 515.

While in the component group 520 the exertion variables ascertained inthe circulatory system were combined, the block 524 serves to unite theoutput variable of the block 520 with a signal designating the actualphysical activity. The output signal of the block 524 thus indicates thecardiac output (HZV) requirement. The output signals of the blocks 515and 520 are to some extent redundant and can be put in relation to oneanother in the subsequent characteristic field in order to increase thereliability.

Of particular significance is an additional transfer component 525,which is included in the telemetry system of FIG. 1. Via this componentgroup, external exertion data ascertained by means of an ergometer canbe fed into the block 524, and by means of external programming both theoutput variable of block 515 and that of block 520 can be set inrelation to the instantaneous load. By insertion of the current exertiondata into the memory locations of the characteristic field in block 525,which locations are addressed by the means of the output signals ofblock 515 or 520, the other signals characterizing the HZV requirementcan be monitored or calibrated, so that the reliability of the systemcan be increased or a regulation brought about. By the transfer andcalibration of the exertion signal available outside the body with thecorresponding intracorporeally obtained signal, a possibility forcalibration or a linkage for regulation can be obtained.

Two further measured value pickups 508 and 509 ascertain signals whichlikewise relate to the cardiac output. In the illustration in FIG. 5,the measured value pickup 508 for the stroke volume represents (via thesystolic intervals as a pressure pickup or microphone or by means ofimpedance cardiography or a combination of the two methods) a standardfor the volume adaptation of the heart as a reaction to a predeterminedphysical exertion. The further measured value pickup 509 for the Q-Tinterval ascertains a standard for the current rate requirement from thesignals picked up in the heart at the pacing pulses, likewise by meansof a corresponding characteristic field. Following a correspondinganalog/digital conversion in conversion blocks 513 and 514 and anoptional non-linear distortion of the transfer behavior are blocks 518and 519 containing characteristic field groups, the combination of thevariables determining the rate takes place in a block 526.

The linkage of the variables characterizing an HZV requirement iseffected in block 527, and depending on the programming of block 527various linkages can be selected:

The output variables of blocks 524 and 526 can be superimposed on oneanother and control the heart rate directly (as the basic rate of thedemand pacemaker 503). This control can be performed taking into accountthe instantaneous stroke volume ISV (arrow from block 518 to 527), sothat all the variables that have an influence on the heart rate areprocessed in combined form, and a favorable cardiac output for theinstantaneous rate based on the ascertained variables is established.The additional evaluation of the stroke volume in block 527 can be donewith a different weighting than that fed into block 526 as a trend forthe rate to be adhered to, so that in particular, regulationfluctuations can be avoided here. If a great number of variables thatmust be ascertained in a stable fashion are present, then optionally thestroke volume can be left out entirely from the processing in block 526.The same applies to the variable Q_(T).

In a corresponding manner, the pacemaker can also be used in regulatedoperation, where only the linkage in component 527 needs to beconverted. To this end, the HZV requirement in the characteristic fieldof block 527 is calibrated with the product of the stroke volume and theinstantaneous rate, the rate being raised or lowered until the productof the stroke volume and the stroke rate corresponds to the cardiacoutput predetermined by the block 524. It is apparent that by means ofdifferent linkages, various control or regulating mechanisms can berealized, and in particular within the characteristic field the rate canbe varied incrementally by means of a search strategy in such a mannerthat the largest possible cardiac output is attained.

An additional error recognition means 528 shuts off the signals pickedup in the heart if faults are ascertained there, and the error criteriacorrespond to those that in demand pacemakers prevent control of thepacemaker by the heart.

An arrow from the output of block 527 and pointing toward the parametermemory 504 indicates that the programmed parameters of the pacemakerundergo variation. Among these is in particular an expansion of theprogrammed time variables, such as refractory or blanking times withdecreasing frequency. This relationship can be related generally to thetime control of the pacemaker. The programmable variation in block 504is effected preferably by means of a characteristic field stored inmemory there, the memory of which, containing the programmed operatingvalues of the pacemaker, is addressed by means of a variable derivedfrom the frequency.

The pacemaker 503 is in particular a single-chamber pacemaker forventricular stimulation, because in this way it is unnecessary to placean additional electrode in the atrium. The measured value pickup forfurther physiological variables are disposed in the pacemaker housing orin the ventricle electrode, so that the implantation technique does notdiffer from the conventional pacemaker, or is even simplified ascompared with AV pacemakers.

FIG. 5a shows how by means of the external communication unit theindividual characteristic fields 532-534 are addressed in thecorresponding cells--as described above--and data located there are readout or new data are read in. The addressing is effected independently ofthe other operation of the cardiac pacemaker 535, which is determined bynonphysiological data, and during the programming of the physiologicalportion this control is rendered inactive (fixed-value signal). Thebasic pacing rate and the other physiologically determined operatingparameters are fixed during the programming to a value corresponding tothe resting state of the patient.

As a special feature it is also provided that by means of theconfiguration data (characteristic field 534) contained in thepacemaker, which data define the data linkage of the characteristicfields, a graphic representation is called up, which corresponds to thisconfiguration. The individual characteristic fields are represented asblocks on a screen or LCD screen and can be called for programming bydialing with a light wand or by means of pressure in the case of atouch-sensitive display. The particular characteristic field called up,or the corresponding component, then appears enlarged on the screen, sothat the data fields marked with a cursor can be changed. To facilitateprogramming, arbitrary individual structures of the linkage diagram canbe called up and varied using the so-called "windows" technique. Herenot only data sets but also, depending on the access authorization ofthe communication portion, configurations of the processing (input andoutput linkages) can be changed as well, so that the system is extremelyflexible and can be tailored to an individual patient in accordance withthe empirical values obtained. For calling up the graphic representationof the screen configuration, either the data of the configurationcharacteristic field are used for direct addressing of a correspondingmemory region, or a corresponding block circuit diagram is synthesizedbased on the pertinent linkage information, using CAD techniques.

It is particularly advantageous here that the communication system showncan be incorporated in a standard type of data processing system (PC orthe like), and the communication interface with the pacemaker isprovided by an additional assembled circuit board that can be insertedinto the PC, which is furnished along with the associated software thatcontains the above-mentioned functions in programmed fashion, so thatthe communication portion in an existing PC entails only slightadditional cost. Nevertheless--depending on the existing expansion ofthe PC--a very great processing capacity is available, which enables thesimultaneous call-up and representation of even complex illustrations,and the operator guidance provides the user with instructions andwarnings for the configuration programming of the system. Via a printer,a protocol relating to the programming process is prepared, whichdocuments the set operating state of the pacemaker. The programmed datainputs for the configuration can simultaneously be stored in a centralmemory, so that the operating parameters of the particular pacemaker canpreferably also be called up via external data communication options andin emergency cases be available to any physician. The programmingportion is designed in particular as a communication terminal, so thatcomplex software that also relates to operator guidance and to theconfiguration of the pacemaker is centrally stored in memory andtransferred to the particular communication terminal. In this way it isassured that in programming, the latest software is used, so thatfurther development--taking into consideration the particular hardwaresituation--can be done even after the implantation. Experience with aparticular pacemaker type in a great number of patients withcorresponding clinical pictures thus contributed subsequently tooptional further development or improvement of the already implantedsystem.

The illustration shown on the screen of the communication unit forinstance corresponds to a block diagram such as that shown in FIG. 5.

The characteristic fields shown in FIGS. 6a-6c provide examples forrelationships, stored in memories having a matrix organization, betweenvariables such as are used in the abovedescribed pacemaker concept. Therepresentation is preferably done in a three-axis coordinate system, sothat a perspective graphic illustration in the external control unit canbe provided. If only two coordinate axes are used, then the illustrationwill be in two dimensions. An additional illustration option is providedby superimposing two characteristic fields in one diagram. Tostandardize the triggering, the characteristic fields selected here arebased on three-axis systems, because the associated memory is thendesigned as a two-dimensional matrix, so that the correspondingnumerical values are likewise capable of being illustrated in twodimensions, that is, on the screen, and thus are variable either bymeans of graphic entries made with a light wand or by numerical inputwith cursor addressing.

In the characteristic field shown in FIG. 6a, the numerical values K1and K2 can be two different input variables, which are linked, or theymay be one measured variable and one parameter--for example, the currentheart rate or the blood temperature. Thus a non-linear characteristiccurve of a measured value pickup with temperature correction can beperformed.

By superimposing two characteristic fields, a calibration in which thetwo characteristic fields are matched spatially with one another can berealized, or a regulation of a predetermined strategy, which forinstance comprises making the volume between two superimposedcharacteristic fields, or the dependent variable is sought by means ofincremental variation of an independent variable a relative or absolutemaximum. In the last-mentioned case, the independent variable representsa measured value, wherein the dependent variables are varied inaccordance with the strategy and the variation is monitored inaccordance with a differential criterion.

In a further embodiment, one of the axes is the time axis, so that bymeans of the characteristic fields heart events in the past are storedin memory by means of the characteristic fields and are transferrableout of the heart to the control unit with the same graphic illustrationmeans that also pertain to the rest of the pacemaker system.

Correspondingly, the time-dependent behavior of the pacemaker can beillustrated in the control portion, by graphic means, as a function ofheart events, as is known in conventional pacemakers from therepresentation of the pacing rate as a function of the followupfrequency of spontaneous heart actions. While in the control functionsthe characteristic fields are thus firmly programmed, in the regulationthey serve as memories for the variable values, which are used as abasis for the regulating criterion; the regulating operation makes thestatus of the system graphically clear to the attending physician bymeans of graphic representation of the current field of the mostrecently run-through values. By corresponding programming, the system isswitchable--as described--at any time between an open-loop controlsystem and a closed-loop control system. This switchover can be doneautomatically as a function of preceding signals, if a correspondingcharacteristic field association is provided.

In FIG. 6b, in a further characteristic field, the cardiac output isshown as a function of the heart rate and in [sic] the stroke volume.This characteristic field has particular significance for thecontrolling of the pacemaker, because the cardiac output is a standardfor the performance capacity of the heart, especially since thevariation of the heart rate by itself is not a sufficient criterion, ifthe attainable stroke volume is left out of consideration. Thecharacteristic field shown in FIG. 6b shows the purely mathematicalrelationship that is attained by calculation, where two different loadcurves L1 and L2 are plotted on the precondition that a constantphysical load must be countered, in the control of the pacemaker, with alikewise corresponding cardiac output. The stroke volume is variablyshown between the minimum and maximum physiologically allowable values,and the same is true for the heart rate. For the pacemaker, however,only the heart rate can be influenced, while the stroke volume isestablished automatically is accordance with the existing adaptabilityof the heart. That is, it furnishes on the one hand, as a product withthe heart rate, a standard for the current performance of the heart,while on the other hand a decrease or increase--with respect to aconstant heart rate--is a criterion that the intracorporeal regulatingsystem desires an increase or decrease in the cardiac output, as long asthis adaptability is still present in the particular patient.

To enable better evaluation on the part of the physician as to whatconsequence the individual open- or closed-loop control variables andoptionally a correspondingly selected operating characteristic curvehave for the control, the illustration of FIG. 6c is provided. Here, ina further characteristic field, the dependency of the stroke volume onthe heart rate and on exertion is shown; the axial direction has beenselected in accordance with that in the characteristic field of FIG. 6b,to enable simpler comparison. It is demonstrated here that the strokevolume, in the case of restricted adaptability of the heart rate--asshown here--is limited toward higher values, and toward higher frequencyvalues the stroke volume decreases, because the chamber fillingdecreases, in particular in the ischemic heart. By superimposition ofthe values of the corresponding diagrams, the operating range of thepacemaker is to be defined, and in the case of automatic adjustment bycharacteristic field super-imposition, the point of departure is thatthe external exertion variable must not be allowed to deviate by morethan a predetermined amount from the cardiac output, if the performancecapacity of the heart is to be adequate to exertion over the long term.

The solid line in the illustration shows that an overly great increasein the heart rate (characteristic curve with slight upward slope withrespect to the axis HR) leads to a drop in the cardiac output and istherefore not favorable in the case shown. Contrarily, the plottedcourse of a characteristic curve is favorable, in the event that theexertion of the particular patient must continue to be limited becauseof the restricted volumetric adaptation of the heart. If thecharacteristic field of FIG. 6c extends to higher rates HR,contrarily--as shown in dashed lines--then the operating characteristiccurve can be selected flatter toward higher heart rates [and] a regionwithout reduction of the stroke volume is attainable, in which thecardiac output is correspondingly increased. If there are times ofspontaneous activity of the heart, then the operating characteristiccurve of FIG. 6c is ascertained by ergometric exertion of the patientduring spontaneous actions, and in the pacing instance is usedaccordingly, using the stroke volume as a control variable.

In the case where there is additional knowledge of measurement variableswhich--as described--enable [sic; word missing] the requirement of thecardiac output on the basis of current physiological exertion data ofthe heart, a further possibility for control exists, wherein in thiscase the working points resulting on the basis of the stroke volume thatis established as shown in diagram 6c and the working points resultingon the basis of the required cardiac output as shown in FIG. 6b aresuperimposed, and an average is taken based on the weighted data;however, an allowable rate range can be predetermined, which resultsfrom the comparison of the diagrams of FIGS. 6b and 6c, under theaforementioned conditions that the cardiac output and the exertion inthe characteristic field should not deviate substantially from oneanother.

The characteristic field according to FIG. 6c is in particular laid outsuch that rate ranges in which increasing load [sic; word missing] areduction of the stroke volume (with respect to the corresponding strokevolume at a higher rate), are to be circumvented, because in such a casea higher rate value leads to a better cardiac performance. Theserelationships, however, are readily apparent in the characteristic fieldrepresentation, and the attending physician can make optimalarrangements by using the control unit having the possibility for agraphic display.

An additional favorable application of the characteristic fields shownhere is in the graphic monitoring of adaptation of the programmable timeconstants. Here measured variables that are associated with timeconstants--for instance thermal regulation of the circulation, takingthe blood value into account--are [sic; no remaining verb in sentence].In this case, with an external abruptly increasing exertion, the rise inthe blood temperature is monitored by comparative measurement andchronologically displayed, and the "programmable time constant"contained in the corresponding processing component group is now variedin such a way that the theoretical course resulting therefrom is adaptedas much as possible to the actual time behavior, and in the three-axisperspective characteristic field display the variation of one parametercan be taken into account as additional independent variables.

In FIG. 6, with the aid of the diagram known from the foregoing drawingfigures, the linkage of the control of the heart rate by means of aplurality of input signals in shown in accordance with an exclusive ORlinkage. The illustration is at the same time an example of a systemconfiguration in which the signal processing method is dependent on asignal event itself. The heart rate is influenced first in a mannerlinked to the stroke volume, as described above. In the case of thearrow shown in the diagram, however, it is presumed that the variationof the stroke volume in the particular patient (or a correspondingvariable) is usable only to a limited extent for controlling the heartrate.

In the case of the rate R₁, it is assumed that there is an intrusion I,resulting in a rise of the exertion B in the peripheral region of theuseful field, without the rate R₁ reducing the stroke volume to a valueadequate for this exertion. In the case of a heart rate influencedsolely by the stroke volume, the rate would attain a maximum value R₀,and upon an increase in the exertion would decrease again, because thestroke volume undergoes an intrusion toward the frequency R₁, anddecreases from R₀ on, which in turn leads to another rate reduction.Thus in this case R₀ represents the upper rate limitation of thepacemaker.

In order in this case as well to offer the patient a physiologicallycorrect control, a further load-related parameter of the pacemaker (forexample, the blood temperature) is additionally utilized for control.The blood temperature picked up is converted in a correspondingcharacteristic field into the associated exertion level B, which islinked by means of an OR relationship with the output signal of thecharacteristic field which contains the rate programmed in accordancewith a variable correlated with the stroke volume, so that the controlof the heart rate is taken over by the blood temperature, if uponattaining a certain temperature level an associated heart rate is notattained. In the graphic display presented to the physician formonitoring, the exertion level as a function of the temperature isrepresented by a horizontal surface, which shifts by level. If the levelexceeds an exertion value that is greater than a corresponding exertionthat is adequately covered by the cardiac output resulting at the heartrate stroke volume, then the temperature sensor takes over the task of"guidance", in that the heart rate is now influenced such that thecardiac output is adapted to the direction.

This corresponds to a switchover of the outputs of the characteristicfields in the manner of an OR linkage. The variable linked to the strokevolume now serves with the product of the heart rate for ascertainingthe actual cardiac output, and the heart rate is raised enough that theattainable cardiac output is again equivalent to the exertion. This isthe case at the rate R₂. The control shown by means of superimpositionof two physiological parameters results in a relatively rapid runthroughof the rate range from R₀ to an R₂ in the patient with increasingexertion, so that at all times an adequate cardiac output for theexertion is made available.

Referring to the diagram shown in FIG. 6e, an exemplary embodiment willbe explained, in which the switchover to various physiologicalparameters for the sake of controlling the heart rate is done not as afunction of a picked up parameter, but rather as a function of the heartrate. In the physiological course represented in the diagram shown, avariable characteristic of the stroke volume no longer varies beyond acertain heart rate, even though at higher rates a stroke volumeadaptation still takes place. This can for instance happen if the signalPEP (presphygmic period) is also used for the rate control, while LVET(systolic discharge time) is initially not taken into account, but doesincrease further with increasing exertion. In this case, a controlexclusively as a function of PEP would means that the physiologicalregulation would become effective up to a certain heart rate range.Above this value, an exertion adaptation takes place only by means of aphysiological stroke volume adaptation, which in the case of peakexertions can lead to an unsatisfactory adaptation behavior. A changedprogramming of the characteristic curve (F1) in the operating range thatis available does not produce any change here, because with a lower risein the heart rate as the PEP increases, only the stroke volumeadaptation based on LVEP is utilized to a greater extent already atlower rates. In this case (as described for the diagram shown earlier),use is made of the fact that by means of an additionalperformance-related physiological parameter ascertained in the body ofthe patient, the heart rate is additionally raised upon exertionwhenever the product of the stroke volume and the heart rate is nolonger adequate for the physical exertion. To this end, however, ameasured variable must then be picked up which is correlated exactlywith the current stroke volume, while the characteristic variable PEPpicked up here furnishes information for only a portion of the strokevolume adaptation. In that case, a characteristic field is used which asa function of the current heart rate effects a switchover to the controlby means of another parameter. The signals PEP and LVEP here formsignals picked up by means of acoustic receivers in the heart chamber,these signals being representative for the stroke volume.

Above a predetermined heart rate HR, the heart rate is thus controlledby the blood temperature, so that an additional heart rate increase withincreasing exertion is possible, which permits a further heart increase.In this case, by means of a suitable programmed characteristic fieldwhich as data contains a linkage instruction for differentcharacteristic fields in programmed form and to this end assures thatabove a predetermined rate level the blood temperature, at a value thatcorresponds to a major physical exertion, contributes to the furtherrate increase, so that the cardiac output is adapted to the actualexertion, and the additional adaptation capability of the stroke volume(which with control by PEP does not need to be ascertained) also formsan additional reserve at higher rates. The blood temperature, forinstance as a differential value, will generate an additionalprogrammable relative variation of the heart rate, so that noconsideration need be taken of measurement deviations inherent in theabsolute values. (An additional measurement of the absolute strokevolume is possible, for example, by electroplethysmographicmeasurement.)

A control of this kind has the advantage that brief adaptations of thestroke volume do not lead to excessive jumps in the rate, yetnevertheless an additional adaptation of the cardiac performance toexertion is possible in the case of a long-lasting major physicalexertion (the blood temperature rises in a delayed manner).

In the case of regulation with the cardiac output as the referencevariable, where the current stroke volume is used together with anexertion variable as an address for the rate data in the characteristicfield, a corresponding rate increase takes place once again, and LVET orsome other stroke-volume-dependent measured variable (preferablyimpedance cardiography) should be used, in order to attain the strokevolume adaptation in the range of greater exertion as well. It will beunderstood that in accordance with signal levels, in the mannerdescribed, other signal linkages (open-/closed-loop control) are alsovariable.

The foregoing description shows that the linkages in terms ofmeasurement technology by means of programming of the system on the onehand exactly determine the technical function of the system and make itinto an automatic control or regulation system - but on the other hand,the attending physician can monitor the functioning of the system at anytime and intervene as needed by monitoring the memory instructions. Theinvention is not restricted in its scope to the example described above.Instead, a great many variants are conceivable, which make use of theprovisions described even with fundamentally different kinds ofembodiments. In particular, the invention is not restricted torealization using discrete logical component groups, but instead canadvantageously also be realized with programmed logic--in particularincluding the use of a microprocessor.

I claim:
 1. A cardiac pacemaker, comprising:means for applyingstimulating pulses to the heart of the patient at a rate determined by apacing parameter; means for detecting a first physiological parameterwhich is correlated with physical exertion of the patient and producinga first output signal representative of said first physiologicalparameter; a memory having a plurality of memory locations containingdata; a means for producing a first address signal as a function of saidfirst physiological parameter; a means for producing at least onefurther address signal; a means for addressing said plurality of memorylocations as a function of said first address signal and said furtheraddress signal and for outputting the addressed data as a second outputsignal; circuitry means receiving said first output signal for varyingthe pacing parameter as a function of said first output signal, saidcircuitry means being controllable by the addressed data received bysaid circuitry means.
 2. A cardiac pacemaker as defined by claim 1,wherein the data contained in an addressed memory location can be readout and used as said selection control signal.
 3. A pacemaker as definedby claim 1, wherein input signals are written in the form of data inaddressed ones of said plurality of memory locations.
 4. A pacemaker asdefined by claim 1, wherein each said second output signal representspolling data which activates auxiliary memories that contain a pluralityof data.
 5. A pacemaker as defined by claim 4, further comprising anexternal communication means, and an auxiliary memory which isaddressable by said external communication means.
 6. A pacemaker asdefined by claim 5, wherein said auxiliary memory stores information inthe form of data which when accessed become command signals whichdirectly affect at least one operating parameter of said circuitrymeans.
 7. A pacemaker as defined by claim 4, further comprising anexternal communication means and auxiliary memories which contain datathat can be read out by said external communication means.
 8. Apacemaker as defined by claim 1, further comprising external control andcommunication means for individually reading in and out and changing ofthe data of the individual memory locations of characteristic valuememories.
 9. A pacemaker as defined by claim 8, wherein said externalcontrol and communication means include graphic reproduction means whichrepresent the memory contents as a function of signals forming theaddresses.
 10. A pacemaker as defined by claim 1, wherein said circuitrymeans includes a microprocessor means for performing serial processingof information retrieved from said memory.